@Dan Sheppard I have uploaded a new save game file, from just before the season changeover. It's called "wrt_gillingham_missing_income-may25.fmv". No more season ticket income appeared for that season, I only received more when it moved to the next season. I've attached a screenshot where you can see the Income once I'd moved into the new season for season tickets is over £1.4million but for the previous season remained just £93,223.
To summarise, at the start of the very first season, £841,280 was recorded as Season ticket income, then nothing after. At the start of the second season £93,233 for season ticket income, then nothing after. Now as I start a third season, £1,487,244 has come in as season ticket income.